The present invention relates generally to lasers diodes and, in particular, to an assembly that includes a laser diode array, an integral memory device storing operational information about the laser diode array, and an integral processing device that records information to and retrieves information from the memory device.
Semiconductor laser diodes have numerous advantages. They are small in that the widths of their active regions are typically submicron to a few microns and their heights are usually no more than a fraction of a millimeter. The length of their active regions is typically less than about a millimeter. The internal reflective surfaces, which are required in order to produce emission in one direction, are formed by cleaving the substrate from which the laser diodes are produced and, thus, have high mechanical stability. Additionally, high efficiencies are possible with semiconductor laser diodes with pulsed junction laser diodes having external quantum efficiencies near 50% in some cases.
The cost and packaging of laser diodes are problems that has limited their commercialization. It is only recently that both the technology and availability of laser diode bars, and a method for packaging them, has made two dimensional laser diode pump arrays a commercial reality. One technique for producing such a two dimensional laser diode array is demonstrated in the U.S. Pat. Nos. 5,040,187 and 5,128,951 to Karpinski. Also, newer techniques have been used to make more efficient an older packaging approach whereby individual diodes are sandwiched between two metallic foils. The advent of lower cost laser diodes and efficient packaging has led to the possibility of producing very large, solid-state laser systems which use many pump arrays.
While laser diode pump arrays have a relatively long life when compared to the traditional flash-lamp or arc-lamp pump sources, they are still considered consumable items that require periodic replacement. In some cases with modularized laser diode arrays, one may even wish to replace only a portion of the array. For pulsed lasers, the number of shots which the laser diode arrays have fired is recorded. For continuous-wave (CW) lasers, the amount of time the laser diode arrays have operated (time-on) is of interest. Typically, these values are monitored and stored within the external electronic control systems which operate these laser systems. These electronic control systems must contain a shot-counter or time-on counter for each laser diode pump array to determine the relative age of each laser diode array thereby permitting the development of a replacement schedule for each laser diode array. However, when a laser diode pump array is replaced, these shot-counters or on-timers must have the ability to be reset to zero if a new laser diode array is used. If a used laser diode array is installed, then these shot-counters or on-tirers must have the ability to be reset to a predetermined value. Furthermore, when a laser diode array is removed from a system for replacement, a difficulty arises in that there is no longer a shot count or on-time associated with the pump array, unless written records are meticulously kept.
In addition to the shot-count, there is other information about a diode array that is of particular interest, such as the serial number of the array, the number and frequency of over-temperature fault conditions, and the voltage drop (i.e. the resistance rise) across the array. These characteristics are useful for selecting an application for a used laser diode array, or for determining the causes of its failure. These characteristics are also important for warranty purposes. However, the operator of the system has no interest in recording these data since it may limit his or her ability to rely on the warranty when a failure arises. On the other hand, the manufacturer has a keen interest in knowing the operational history of an array for warranty purposes.
When semiconductor laser diodes are used as the optical pumping source for larger, solid-state laser systems, the emitted wavelength is critical. Laser diode pump arrays achieve efficient pumping of the laser host material (e.g. Neodymium-doped, Yttrium-Aluminum Garnet) by emitting all of their light energy in a very narrow spectral band which is matched to the absorption spectrum of the gain media (i.e. slabs, rods, crystals etc.), typically within 2-6 nanometers full-width at the half-maximum point (fwhm). The laser diode pump array emission wavelength is a function of the temperature at which the pump array is operated. The pump array temperature is a complicated function of many interrelated variables. The most important of these variables are the temperature of the coolant flowing to the diode array, the operational parameters of the diode array, and the configuration of the heat exchanger on which the laser diodes are mounted. The operational parameter of a CW driven array is simply the drive current. But for pulsed laser systems, the peak drive current, the repetition rate, and the pulse width of the drive current are all important operational parameters. Because the performance of the laser diode array changes during the service life of a laser diode array, the host external system controller has to compensate for any degradation of performance (output power or wavelength) by modifying these input operational parameters except for the heat exchanger configuration. Often, the altering of the operational parameters requires manual calibration of the arrays using external optical sensors. This is a tedious job and requires a skilled technician who understands the ramifications of modifying the interrelated variables which change the output power and wavelength. Even when the laser diode array""s operational parameters are properly calibrated, rapid changes in the performance of the laser diode array may go unnoticed until the next scheduled maintenance. This manual calibration also is often required during the initial installation of the laser diode array assembly.
Therefore, a need exists for a laser diode array assembly that includes an integral means for recording operational events and maintaining this information with the assembly throughout its service life. It would also be beneficial for this laser diode array assembly to have the capability of instructing the external laser operating system on the input drive parameters that should be used to provide for optimal output of the laser diode array assembly.
A modular laser diode array assembly includes at least one laser diode array, an intermediate structure on which the array is mounted, and an integral memory device. The laser diode array has a plurality of laser diodes which are in electrical contact with at least one other of the plurality of laser diodes. The assembly further includes means for supplying external power to the laser diode array. The memory device stores operating information for the laser diode array and is mounted on the intermediate structure which may be a printed circuit board. The memory device communicates with an external operating system. After the assembly is installed in and connected to the external operating system, a system controller accesses the memory device to obtain the operating information (temperature, input power parameters, etc.) which enables the system controller to properly apply power to, or set conditions for, the laser diode array.
In another embodiment, the assembly includes sensors for sensing the operating conditions experienced by the laser diode array. The external operating system monitors the sensors to assist in determining the operational parameters at which the system is to be operated. These sensors may be optical power sensors, optical wavelength sensors, electrical input power sensors, temperature sensors, vibration sensors, etc.
In yet another embodiment, the assembly includes processing means that communicates with the external operating system. The processing means is coupled to the sensors for directly monitoring the operating conditions of the laser diode array and is also coupled to the memory device. Based on the operating conditions monitored, the processing means instructs the external operating system to supply the optimum operating parameters. Thus, the assembly is self-calibrating in that it monitors the operating conditions and instructs the external operating system to provide input power in a manner that allows for the optimum output.
Using the integral memory device and the processing means provides numerous benefits. For example, the shot-count or on-time value becomes physically a part of the assembly as it is stored within the integral memory device. This integral memory device could then be read from and updated, as necessary, by the control electronics of the external operating system or the processing means when one is used.
There are many additional pieces of data which could be stored in this memory device, such as: the array serial number; the number and times of fault conditions such as over temperature or activation of protection circuitry; the voltage drop across the array and the time of the occurrence if it changes significantly (this may be an indication of individual laser bar failures); and the array""s spectral and power response to different operational conditions. The memory device may also record the ambient environmental conditions such as the ambient temperature, the ambient shock environment, ambient humidity, or electrostatic discharge (ESD) events resulting from the environment around the array.
The above summary of the present invention is not intended to represent each embodiment, or every aspect, of the present invention. This is the purpose of the figures and the detailed description which follow.